Generally in packaging of a semiconductor chip, it is necessary to carry out a step of connecting electrodes formed on the semiconductor chip and external terminals or lead wires with each other. In this step, the electrodes of the semiconductor chip and the external terminals or the like are connected with each other with interposition of a brazing filler metal of gold or tin, an anisotropic conductive film or resin such as a conductive adhesive.
At this time, a tool tip is employed for locating and pressing the semiconductor chip on and against prescribed positions of the external terminals or the like and directly heating the brazing filler metal of gold or tin or the anisotropic conductive film or indirectly heating the same through the semiconductor chip.
For the tool tip, there are two types of heating systems, namely a constant heat system of regularly heating the same to a required temperature and a pulse heat system of instantaneously heating the same only as needed in response to the bonding specification of the semiconductor chip.
In either heating system, high accuracy is required of a pressing surface on the forward end of the tool tip as a consequence of high densification of packaging of the semiconductor chip. Since temperature distribution of the pressing surface in heating is homogeneous and flatness of the pressing surface is excellent from this requirement and the homogeneity of the temperature distribution and the flatness can be maintained over a long time, a technique of sticking a diamond film to the pressing surface on the forward end of the tool tip is employed.
In case of the pulse heat system, however, there is such a problem that heat response is inferior as compared with a tool tip consisting of a pure metal such as nichrome, molybdenum, inconel or stainless steel to which no diamond film is stuck since temperature rise of the diamond film stuck to the pressing surface on the forward end results from heat transfer from a tool base material.
Namely, the tool tip employing a diamond film requires a long time as compared with the tool tip consisting of a pure metal for heating and cooling the pressing surface on the forward end of the tool tip to prescribed temperatures in response to current pulses. Therefore, it is difficult to reduce the time required for single bonding of the semiconductor chip.
In relation to this point, there has been proposed a method of making a diamond film synthesized by a vapor-phase synthetic method on a pressing surface on a forward end of a tool tip conductive so that the diamond film itself will generate heat, and the problem related to heat response is solved in Japanese Patent Laying-Open Gazette No. 5-304191 or Japanese Patent Laying-Open Gazette No. 5-226421.
Also U.S. Pat. No. 5,488,350 proposes to employ a conductive diamond film synthesized by a vapor-phase synthetic method as a heat generator.
The technique disclosed in the aforementioned Japanese Patent Laying-Open Gazette No. 5-304191, however, employs a structure in which the diamond film is brazed to a tool base material of a metal whose coefficient of thermal expansion is different. Hence, there are such problems that distortion takes place in the diamond film due to difference of thermal expansion in temperature rise and flatness of the pressing surface on the forward end of the tool tip is hard to ensure.
According to the technique disclosed in the aforementioned Japanese Patent Laying-Open Gazette No. 5-226421, there are such problems that the cost for the tool tip increases and the tool tip is easy to break in handling thereof since the material used for the tool tip itself is diamond.
According to the technique disclosed in U.S. Pat. No. 5,488,350, further, the conductive diamond film is formed in a pattern similarly to a heater wire, i.e., the conductive diamond film is selectively grown in order to homogenize temperature distribution of the heat generator. Therefore, SiO.sub.2 or the like is formed on a substrate or insulating diamond in a reverse pattern shape relative to the pattern of the conductive diamond film through sputtering or the like, for forming the conductive diamond film by employing this as a mask. However, it is necessary to carry out this formation process by controlling the film thickness of SiO.sub.2 with high accuracy. Further, there are such problems that a step of dissolving/removing SiO.sub.2 is required after forming the conductive diamond film and the tool tip manufacturing cost increases.